The present invention relates to replenishment of ink jet print heads which utilize ink that is converted from a solid state to a liquid state within the print head.
In the printer art, the use of inks, generally known as phase change or hot melt inks, which are heated to place them in the liquid state for application to a substrate is finding growing acceptance in view of a number of advantages offered by such inks.
A print head using such an ink includes a reservoir for storing a supply of the ink together with a heating element for maintaining the ink in the liquid state.
Since the length of time during which a printer can operate continuously depends on the quantity of ink stored in the reservoir, it would be desirable, from the stand point of productivity, for the quantity of ink stored in the reservoir to be as large as possible. However, as the ink storage capacity of a print head increases, so does the moving mass represented by the print head, and this increases the problems associated with displacing the print head at high speed and isolating the remainder of the printer from the forces generated by these displacements. Moreover, as the mass of ink stored in the reservoir increases, so does the energy required for maintaining the ink in the liquid state.
These problems are exacerbated in color printers whose print heads must be provided with a supply of inks of three or four different colors.
In an effort to resolve the conflicts between the desire to operate a printer continuously for long periods of time and the desire to minimize the moving mass represented by the print head, various arrangements for automatically replenishing the print head reservoir have been proposed. Examples of such arrangements are disclosed in U.S. Pat. Nos. 4,593,292; 4,636,803 and 4,667,206. The arrangements disclosed in these patents have in common that the replenishment operation requires a relatively complex mechanism which is itself subject to breakdown and which has a limited storage capacity. Moreover, if it were possible to adapt any of these known systems to a color printer, essentially a separate system with a separate drive device would be required for each ink color.